CROCODILES OF THE TEXAS CRETACEOUS; THE CAMPANIAN OF BIG BEND TO THE CENOMANIAN OF NORTH TEXAS, A COMPARISON OF GREAT SIZE, FEEDING BEHAVIOR AND PALEOECOLOGY

Deinosuchus is the best documented giant crocodyliform from the Cretaceous of North America, and among the best known of the fossil fauna of Big Bend National Park. Reported by Colbert & Bird as Phobosuchus from the Campanian Aguja Formation of Big Bend in 1958, it has since held the record of being the only large crocodyliform from the Cretaceous of Texas. Here we report a new large crocodyliform from the Cenomanian (95Mya) Woodbine Formation of North Texas and compare the behavior, environments and ecology of these two Texas giants.

The new Woodbine crocodyliform was discovered in northeastern Tarrant County at the Arlington Archosaur Site (AAS). During the Cenomanian, North Texas was situated along a subtropical coastline, similar to the Florida Everglades. A portion of this coastal ecosystem is preserved at the AAS within the delta plain mudstones, carbonaceous shales and a fossil rich peat bed. A diverse fauna of dinosaurs, crocodyliforms, turtles and lungfish have been recovered. Some of the fossil specimens recovered from the peat bed exhibit tooth marks diagnostic of feeding by a large crocodyliform. Feeding traces consist of pits, scores, and one puncture that occur on multiple turtle shell fragments and two ornithopod dinosaur limb bones. Marks on the turtle shells suggest inertial feeding followed by crushing. Marks on the dinosaur bones indicate possible disarticulation, which is consistent with marks produced by living crocodilians. The ecology of AAS crocodyliforms appears quite similar to that of generalist crocodylians inhabiting delta-plains. AAS theropod remains are rather rare and tooth marks absent. Thus AAS Cenomanian crocodyliforms were likely apex predators.

Deinosuchus lived in a coastal plain as evidenced by carbonaceous mudstones, lignite beds, crevasse splay sands and siderite concretions from the distributary channels of the Aguja Formation. Other workers have found evidence of the feeding behavior of Deinosuchus, in which bite marks were noted on turtle shell, theropod and ornithopod dinosaur bones. Tooth marks on theropod bones implies Deinosuchus may have fed on small theropods. Large theropods are scarcely reported from Big Bend, thus from the Cenomanian to the Campanian, giant crocodyliforms were potentially the apex predators of Cretaceous Texas coastal ecosystems.